The invention relates to an extruder comprising an operative unit composed of a cylinder and at least two screw shafts which are rotatably accommodated therein, a gear unit having at least two output shafts, wherein each output shaft, via a connecting element, is connected in a rotationally fixed manner to one screw shaft, a motor which drives the gear unit and is coupled to the gear unit via a clutch, and a controller installation.
As is known, extruders of this type serve for preparing compounds which, in the operative unit or the cylinder, respectively, are processed via one or more screw shafts, also referred to as extruder screws, rotating therein. In only an exemplary manner, mention may be made of plastic compounds which are melted and compounded in the extruder in order to be subsequently further processed, for example for forming plastic granules or in the context of injection-molding or for manufacturing components and similar. In an exemplary manner, mention should furthermore be made of pharmaceutical compounds which serve in the production of pharmaceuticals, for example in the form of tablets. Here too, the corresponding materials are processed and mixed etc. via the screws in the cylinder, in order to achieve the desired homogenous composition of the extruded product. In order to make this possible, one or more installations, such as, for example, corresponding infeed installations, via which the materials to be processed are added in a metered manner, or heating installations, which serve for temperature-controlling the cylinder or the cylinder sections from which such a cylinder is typically assembled, or similar is/are provided on the operative unit or assigned to the operative unit, respectively. Also in the field of foodstuffs, corresponding compounds are often prepared using an extruder.
The drive of the at least two screw shafts is, of course, an essential aspect in the functioning of the extruder, since both the torque of the screws and also the revolutions of the screws, which are relevant to the energy introduced into the material to be prepared, are adjusted via the drive. This takes place via a motor and a corresponding reduction gear unit which is coupled to the screw shaft or screw shafts. The motor is typically coupled to the gear unit via an overload clutch, wherein the overload clutch, having a corresponding given overload on the screws, opens and separates the gear unit from the motor. The in-principle construction and the function of such an extruder are well known.
In the case of an overload, the clutch only opens when the cumulative torque of the two screw shafts that is applied via the output shafts and the gear unit to one side of the clutch is greater than the cut-out torque defined by the concept and the dimensions of the overload clutch. Then, and only then, does the overload clutch open, which overload clutch is a mechanically-separating clutch in which, for example, spring-loaded balls assigned to one side of the clutch engage in corresponding calottes assigned to the other side of the clutch and, when a cut-out torque is applied, migrate out of the calottes, causing the clutch to slip and open, respectively. Therefore, the cut-out torque has to be applied directly to the clutch; as a result, the actual torque given on the screw shafts is somewhat higher, since there is a certain loss of torque in the mechanical train from the screw shafts to the clutch, and respectively a certain time factor also plays a part, since any increase of the torque on the screw shafts is transmitted with some time delay to the clutch. An overload may thus already exist with the screw shafts but not be applied yet to the clutch. This may have disadvantages for the operation of the extruder and, in particular, also for the screw shafts and wear thereof.